RADIOFREQUENCY AND MICROWAVE RADIATION
IN THE WORKPLACE
1. INTRODUCTION
“Radiofrequency (or RF) Radiation” refers to electromagnetic fields with frequencies between
300 kHz and 300 MHz, while “Microwave (or MW) Radiation” covers fields from 300 MHz to
300 GHz. Since they have similar characteristics, RF and MW radiation are usually treated together.
As well, the lower-frequency boundary of RF radiation is often extended to 10 kHz, or even to 3
kHz, in order to include emissions from commonly used devices.
Figure I: The Electromagnetic Spectrum
The frequency of electromagnetic fields is measured in Hz (hertz), or cycles per second.
1 kHz (kilohertz) = 1000 cycles/second. 1MHz (megahertz) = 1 million cycles/second.
1 GHz (gigahertz) = 1000 million cycles/second.
RF radiation is produced by devices such as radio and TV transmitters, induction heaters, and
dielectric heaters (also known as RF sealers). MW radiation is produced by microwave ovens,
parabolic (dish) antennas, radar devices, and diathermy applicators. See Table III, “Sources of
RF/MW Radiation”, on page 4 for more examples.
This guideline gives advice on preventing overexposure to RF/MW radiation in the workplace and
sets out Occupational Exposure Limits which are enforced in Ontario workplaces by the Ministry of
Labour under the general duty clause (section 25(2)(h) of the Occupational Health and Safety Act).
However, this guideline cannot cover all possible situations. The requirements set out in the
Occupational Health and Safety Act must be complied with, and they should be referred to when this
guideline is used.
2. HEALTH HAZARDS
The nature and the degree of the health effects of overexposure to RF/MW fields depend on the
frequency and intensity of the fields, the duration of exposure, the distance from the source, any
shielding that may be used, and other factors.
The main effect of exposure to RF/MW fields is heating of body tissues as energy from the fields is
absorbed by the body. Prolonged exposure to strong RF/MW fields may increase the body temperature, producing symptoms similar to those of physical activity. In extreme cases, or when exposed
to other sources of heat at the same time, the body’s cooling system may be unable to cope with the
heat load, leading to heat exhaustion and heat stroke.
Localized heating, or “hot spots,” may lead to heat damage and burns to internal tissues. Hot spots
can be caused by non-uniform fields, by reflection and refraction of RF/MW fields inside the body,
or by the interaction of the fields with metallic implants, for example, cardiac pacemakers or
aneurism clips. There is a higher risk of heat damage with organs which have poor temperature
control, such as the lens of the eye and the testes.
Other hazards include contact shocks and RF burns. These can result from the electric currents
which flow between a conducting object and a person who comes into contact with it while they are
exposed to RF fields. (These effects should not be confused with shocks from static electricity.)
Some laboratory studies have reported biological effects from RF/MW radiation at field levels
which are too low to cause tissue heating. To date, these non-thermal effects are not known to result
in health hazards in workers. Although we are constantly exposed to weak RF fields from radio and
television broadcasting, no health risks have been identified from this low-level exposure.
3. EXPOSURE LIMITS
Exposure limits for RF/MW radiation are designed to keep the RF/MW energy absorbed by the
body well below the lowest levels associated with demonstrated adverse effects, and to reduce the
likelihood of contact shocks and burns.
Since the RF/MW energy absorbed by the body varies with the frequency of the fields, and since the
rate of energy absorption is difficult to measure directly, the exposure limits are expressed in terms
of frequency-dependent, root-mean-square (RMS) electric and magnetic field strengths, or in power
density units (W/m2). Power density measures the amount of radiating energy crossing a given area
in a given period of time.
Occupational exposure of the whole body to RF/MW fields should not exceed the values in Table I.
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Radiofrequency and Microwave Radiation in the Workplace
Table I: Exposure Limits for RF and Microwave Exposed Worker
Electric Field
Strength;
RMS
(V/m)
Magnetic Field
Strength; RMS
(A/m)
Power Density
(W/m2)
Averaging Time
(min)
600
4.9
--
6
600/f
4.9/f
--
6
10 - 30
60
4.9/f
--
6
30 - 300
60
10*
6
f/30
6
Frequency
(MHz)
0.003 - 1
1 - 10
0.163
0.5
300 – 1 500
0.5
3.54f
0.0094 f
1 500 - 15 000
137
0.364
50
6
15 000 – 150 000
137
0.364
50
616 000/f1.2
0.354 f0.5
9.4 x 10-4 f0.5
3.33 x 10-4
616 000/f1.2
150 000 – 300 000
* Power density limit is applicable at frequencies greater that 100 MHz.
Notes: 1.
Frequency, f, is in Mhz.
2.
A power density of 10 W/m2 is equivalent to 1 mW/cm2.
3.
A magnetic field strength of 1 A/m corresponds to 1.257 microtesla (uT) or 12.57
milligauss (mG).
In addition, workers should not be subject to RF contact shocks or burns. This can be achieved by
reducing stray fields and installing appropriate insulation and grounding, or by ensuring that the
electric current flowing between a worker and an object energized by electromagnetic fields does
not exceed the values in Table II.
Table II: Induced and Contact Current Limits for RF and Microwave
Exposed Workers
Frequency
(MHz)
Induced Current (RMS)
(mA)
Through
RMS Contact
Current (mA)
Hand Grip and
Through Each Foot
Averaging Time
Both Feet
Each Foot
0.003 - 0.1
2000f
1000f
1 000f
1s
0.1 -110
200
100
100
0.1 h (6 min)
Note: The limits in Tables I and II are based on Health Canada “Safety Code 6”, 99-EHD-237
(1999).
Table III shows which sources of RF/MW radiation may expose workers to levels in excess of
Occupational Exposure Guidelines. Measurements of RF/MW levels should be carried out around
sources with the potential to cause overexposure, in order to ensure compliance with the
Occupational Exposure Limits. Measurements are not necessary for sources which do not have the
potential to produce exposures in excess of the Occupational Exposure Limits.
Radiofrequency and Microwave Radiation in the Workplace
3
Table III: Sources of RF/MW Radiation
Source
Frequency (MHz)
Potential for Over-exposure?
0.015 - 0.3
No
1 - 100
(typically 27.12)
Yes
13.56, 27.12, 915, 2450
Yes
Communications Transmitters:
AM Radio
0.535 - 1.605
Yes
Communications Transmitters:
FM Radio
88 - 108
Yes
Communications Transmitters:
VHF TV
54-72, 76-88, 174-216
Yes
Communications Transmitters:
UHF Radio
470 - 890
Yes
Communications Transmitters:
Dish Antenna
800 - 15,000
Yes
27.12
Yes
Cordless Telephone
46 - 5800
No
Cellular Telephone
824 – 850, 900, 1800, 1900
No
10,500 and 24,000
No
915 and 2,450
No*
Video Display Terminal (VDT)
Dielectric Heater
Diathermy Applicator
CB Radio
Traffic Radar
Microwave Oven
*Federal legislation requires that microwave ovens be constructed to meet stringent microwave leakage limits and to
have safety interlocks. When these interlocks are defeated, for example, during repair work, there is a risk of
overexposure to microwave radiation.
4. CONTROLLING RF/MW RADIATION
Engineering Controls
• Sources of RF/MW radiation should be properly shielded to minimize stray radiation.
• Devices which can produce acute thermal injuries (e.g., industrial MW ovens) should have
interlocked doors
• Devices which produce high levels of stray RF radiation (e.g., induction heaters and dielectric
heaters) should be operated remotely whenever possible.
Administrative Controls
• Exposure of workers to RF/MW radiation should not exceed the recommended exposure limits.
• Areas where worker exposure to RF/MW radiation is suspected to exceed the recommended
limits should be surveyed to determine the exposure levels.
• Needless exposure to RF/MW fields should be avoided.
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Radiofrequency and Microwave Radiation in the Workplace
• Exposure times should be kept as short as reasonably possible.
• Potentially hazardous RF/MW devices should be appropriately labeled, and areas of excessive
exposure around them clearly demarcated. Notices with warnings and the necessary precautions
should be posted.
• Electrically-activated explosive devices should not be placed near sources of RF/MW radiation.
• RF/MW devices should not be used in flammable or explosive atmospheres.
• Equipment sensitive to RF/MW radiation, such as telephone switchboards or control panels,
should not be installed near sources of RF/MW radiation.
• Maintenance of devices used to produce RF/MW radiation should be done by qualified personnel
following standard safety procedures. The equipment should be turned off whenever possible.
Personal Protection
• When exposures cannot be reduced by the above methods, RF/MW protective suits, including
head and eye protection, can be used. Suits should be tested to ensure that they reduce worker
exposure to levels below the occupational exposure limits and that they do not pose any safety
hazards (e.g., overheating, shocks, or fire).
Controlling RF Shocks and Burns
• Metallic structures producing contact shocks should be electrically grounded and/or insulated.
• Insulating platforms or shoes (e.g., rubber-soled shoes) can be used to reduce energy absorption
and currents to ground.
• When the above measures are ineffective or not reasonably possible, workers should wear
insulating gloves.
First Aid
• Remove worker from exposure area to a cool environment and provide cool drinking water.
• Apply cold water or ice to burned areas.
• Seek immediate medical attention.
• Severe MW or RF overexposure may damage internal tissues without apparent skin injury, so a
follow-up physical examination is advisable.
Radiofrequency and Microwave Radiation in the Workplace
5
For more information about radiation protection in the workplace, please call the Radiation
Protection Service at (416) 235-5922.
Remember that while complying with occupational health and safety laws, you
are also required to comply with applicable environmental laws.
For further information or assistance, please contact your
local office of the Ministry of Labour.
Produced by the Radiation Protection Service
of the Occupational Health and Safety Branch,
Ministry of Labour. Disponible en français.
ISBN: 978-1-4435-0631-1 (Print)
ISBN: 978-1-4435-0633-5 (PDF)
ISBN : 978-1-4435-0632-8 (HTML)
Date: May 2009